NEET BIOLOGY

Detailed explanation-1: -A mature embryo sac consists of two synergids, one egg cell and three antipodal cells with one nucleus each. Then there is one large central cell that has two nuclei. Hence, a mature embryo sac consists of 7 cells and 8 nuclei.

Detailed explanation-2: -One cell of the nucellus undergoes meiosis to produce four megaspores. One megaspore survives and undergoes three rounds of free nuclear division followed by cellularization to produce an embryo sac consisting of 8 nuclei in 7 cells (Evans & Grossniklaus, 2009; Serbes et al., 2019).

Detailed explanation-3: -Three cells present at the chalazal end of embryo sac are called as antipodals. The large central cell has two polar nuclei. This makes embryo sac 7 celled and 8 nucleate structure.

Detailed explanation-4: -One of the many mysteries surrounding the origin of the angiosperms is the evolutionary origin of the Polygonum-type embryo sac (monosporic, eight-nucleate and seven-celled) that occurs in the majority of flowering plants.

Detailed explanation-5: -The cells of an unfertilized ovule are 8 in number and arranged in the form of 3+2+3 (from top to bottom) i.e. 3 antipodal cells, 2 polar central cells, 2 synergids & 1 egg cell. One sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the large central cell of the megagametophyte.